Serial ATA (Advanced Technology Attachment) is an evolutionary replacement for the Parallel ATA physical storage interface. Serial ATA is a computer bus primarily designed for transfer of data between a computer processor and hard disk and has at least three advantages over Parallel ATA, namely speed, cable management, and Serial ATA's ability of being hot swappable.
There are three interface power states supported in Serial ATA: PhyReady, Partial and Slumber. In PhyReady (or power up) state, the PHY (physical) logic and main PLL (phase-locked loop) are both on and active, and the interface is synchronized and capable of receiving and sending data. Partial and Slumber are two power saving (or power down) modes. In both Partial and Slumber states, the PHY logic is powered, but is in a reduced power state. However, while the exit latency from Partial state is generally no longer than 10 μs (microseconds), the exit latency from Slumber state is generally no longer than 10 ms (milliseconds).
When a Serial ATA interface is idle (i.e., when either a Serial ATA host adapter or a Serial ATA drive is not active) for a period of time, it is desirable to put the interface into a power saving mode. In addition to saving power while in a power saving mode, the interface lifetime may be increased. Preferably, the power state change of the Serial ATA interface is hardware controlled so that communications with high level layers of the interface may be avoided, which may lead to an efficient power saving method when the interface is in idle condition for a programmable period of time.
Thus, it would be desirable to provide a method and apparatus of automatic power management control which automatically puts Serial ATA interface into power up and power down modes.